Propeller for airplanes and dirigible balloons



June 10, 1930.

F. W. CALDWELL PROPELLER FOR AIRPLANES ANDDIRIGIBLE BALLOONS Filed Dec. 22, 1923 INVENTOR BYD' /Zw 4, A

ATTORNEY Patented June 10, 193

rmx' w. CALDWELL, or narrow, 01110,

PBOPELLER CORPORATION, OF WEST 0] PENNSYLVANIA v ASSIGNOR TO THE HAMILTON STANDARD PBOPELLEB FOR AIBPLANES AND DIRIGIBLE BALLOONS Application filed December 22, 1923; Serial No. 682,189.

My invention relates to improvements in propellers designed for use with airplanes employing very large engines, or for dirigible alloons, and my object is to provide a propeller for the purpose, which, while being substantially as strong as those now made, will be materially lighter. Propellers for use with-dirigible balloons or air planes employing very large engines are relatively I sometimes twenty to twenty-five. feet in length. They are now made of laminated wood, solid throughout, and are unduly hea proportioned to their strength.

, I d that it is possible to construct a propeller for the purpose, having a core of a relatively light wood or other material, and with a skin or coating of laminated strips applied to the core, which will be substantially as strong as propellers now made, and at the sametime will bevery much lighter than present (propellers.

In or erthat my invention may be better understood, attention is directed to the accompanying drawing forming a part' of this specification, and in whic c Fig. 1 is a side 'ew of my improved propeller showing in full lines the relatively light core, andin dotted lines the skin or coat- :0 ing of laminated strips and the metal sheathing covering the tip and leading edge of the propeller;

Fig. 2, a detail view illustrating the employment of thin veneer strips to form the coating or skin, certain strips being. broken away to illustrate the strips beneath the same;

- Fi 3, a sectional view on the line 3-3 of Flg. 2, the stri s or veneers at the top being shown after t ey have been applied but before sand paperin and at the bottom showing the finishe outer surface of the pro eller; and

- ig. 4, a erspective view of the metal sheathing w ich may be 'appliedjto the tlp and leading edge oi theimproved propeller.

In these views corresponding parts are rep v resented by the same numerals. I

The propeller 1 is of any suitable deslgn or shape, and comprises a core 2 made preflarge and heavy. and at the present time are HOMSTEAD, P ENNSYLVANIA, A CORPORATION erably of balsa wood. As is known this wood A is extremely light, and, although it inherently has little strength, it constitutes an eflective core for the propeller and prevents buckling under load, giving in efiect, the strength of a short column of material in compression, as

compared to the long column effect which would be obtained from athin wall in compression, without the bracing effect of balsa wood core. Balsa wood is referred, but the core may be made of other llght material suitable for the purpose. To the outside of the core 2, -I apply thin strips or veneer or laminae ofa very tough strong wood, preferably mahogany. These are secured in place by glue. 'Of course, it is understood that sheets or strips of tough strong composition or metal or other suitable material may be used. The illustration is of a propeller constructed, according to the invention, of thin strips or laminae of mahogany 'on the order of 1/64 inch in thickness an applied in layers to the core as follows: Layers 4, 5, 6 and 7 extend the full length of the propeller from tip to tip and are shown roken away to disclose the layers underneath. Layer 8 extends not quite to the tip of the propeller, while layer 9 extends not quite as near the tip as layer 8, and layer 10 not quite as near the tip as layer 9, etc. In this way a propeller is built up, upon the core, having a relatively thin covering or coating of mahogany veneer at thetips which. becomes thicker and thicker toward the hub hole where the desired maximum strength is secured. Fig. 2 merely shows thirteen layers ofmahogan'y veneer by way of illustration, it being understood that in practice very many more layers would be required to give the desired strength. After the several layers have been thus applied, the outer surface is smoothed down or dressed, as with sandpaper, until a uniformly smooth surface-is presented. Layer 15, with the grain transversely of the axis of the propeller, is then glued-on from tip to tip, and layer 16, with the grain longitudinally of the axis of the propeller, is lastly glued on' from tip to tip. Thus'a uniformly smooth surface is presented, as at 16. Fig. 3, which may then be finished oil in the usual manner, or one or more propeller and others substantially transprotective coverings of cloth or other proversely thereof.

tective material applied as desired. This spec' cation signedthis 18th day 01 Layers 5, 7, 9, 11,13 and 16 are shown with December, 1923. 5 the grain extending longitudinally of the FRANK CALDWELL. 7

propeller, so as to resist longitudinal strains due to the centrifugal effect, while the layers 4, 8, 12, and 6, 10, 14, are shown with the grain extending at an an le of substantially 45 to the length of the lade, the angle of each alternately crossing that of the other. These layers 4, 6, 8, 10, 12 and 14, add strength to the propeller to resist transverse and torque strains due principally to the thrust.

1 ,In order to protect the front or leading 80 V 35 Letters Patent, is as follows:

edge and tip' of the propeller from water spray or abrasion of sand, stones, etc., it may be desirable to apply a metal tip or protective sheathing as shown at 17, Fig, 4. This metal tip or protective sheathing may be ap- 8s plied last after the ropeller has been com- Eletely finished, as s own by dotted lines in find in practice that a propeller made i with a balsa wood core and withthin veneer I w coatings of mahogany arranged as explained,

or coatings of a toug strong composition, or suitable metal sheetings, will have substantially the strength of a solid wood, or comno position, or metal propeller as now made, 95

while at the same time the weight will be only about one-third that of the solid propeller.

Having now described my invention, what I claim as new therein and desire to secure by I 1. A propeller for airplanes or dirig'ible balloons, comprising a core of balsa wood and a completely enclosing coating therefor, comprising a large number of thin successive 40 veneers, each progressively shorter lengthm wise, of-strong tough material, said coating being the principal source of structural strength.

2. A propeller for airplanes or diri 'ble 7 balloons, comprising}, core of balsa woo and a completely enclosing coating therefor, com prising a large number of thin successive veneers, each progressively shorter lengthwise, of strong tough wood, said coating being the principal source of structural strength. Ill

3. A propeller for airplanes or dirigible 1 balloons, comprising a core of balsa wood and a completely enclosing coating therefor, comprising a large number of thin successive veneers of mahogany, each progressively short- 1. er lengthwise, said coating being the principal source of structural strength. 4. An improved propeller for airplanes or 6 dirigible balloons, comprising a core of balsa wood and a completely enclosing coating therefor, comprising a. largenumber of thin successive veneers of mahogany, each progressively shorter lengthwise and some of cilsaid layers extending longitudinally of the 

